This invention relates to roll-up doors intended for use in industrial and commercial buildings and structures and, in particular, roll-up doors that include a flexible sheet forming a curtain for closing a doorway and a pair of spaced apart guide channels in which side edge sections of the curtain are respectively movable.
Roll-up doors for industrial and commercial use have been known for some time and, depending on the precise construction of the particular door, such doors can have a number of advantages. For example, light weight vinyl doors can be made to operate relatively quickly while, at the same time, such doors can have a relatively clean, pleasing appearance. Such doors can be relatively quiet in their operation as they can be operated quickly and efficiently by means of a suitable electrical motor and push button controls.
U.S. Pat. No. 4,478,268 issued Oct. 23, 1984 to Copper Cliff Door Manufacturing (1980) Limited, describes a so-called damage-minimizing door for closing a vehicular passageway in which the door is constructed of a tough rubber or rubber-like material. The curtain is secured along its top edge to a curtain winding mechanism that includes a winding drum supported in mounting brackets. The bottom edge of the curtain is connected to a base bar constructed of angle members and a flat bar. In this curtain, the side edges of the curtain can be pulled laterally through the slot mouth formed by each guide channel when a predetermined impact force is applied to the curtain.
The preferred rubber curtain as described in U.S. Pat. No. 4,478,268 has a thickened area extending along each side edge of the curtain. Each guide channel of the door has a throat of reduced width for restricting movement of the thickened edge area of the curtain out of the channel. The throat of the guide channel is narrower than the thickened edge area of the curtain. The thickened edge area can be provided with a sloping shoulder on the side thereof where the thickened area meets the thin main area of the curtain. One difficulty with this known curtain structure is that there can be substantial friction between the thick rubber edges of the curtain and the metal guide channels, particularly if the curtain is subject to significant wind or air pressure on one side thereof and this can result in problems with the operation of this door.
U.S. Pat. No. 4,601,320 issued Jul. 22, 1986 to Douglas Taylor describes an improved industrial door wherein friction reducing devices in the form of plastic strips constructed with ultra-high molecular weight plastic are bonded to the thickened side edge sections of a rubber or synthetic rubber curtain. These plastic strips extend along the side edge sections of the curtain and are provided to reduce the amount of friction between the side edge sections and the guide channels. On one side of the curtain these strips are spaced apart in an end-to-end relationship so that they will not interfere with the raising or lowering of the rubber curtain. Although such plastic strips have worked satisfactorily, a problem with such strips is that the plastic material from which they are made is relatively expensive and the process of bonding the strips in the desired fashion to the door edges is fairly labour intensive and adds significantly to the cost of the door.
U.S. Pat. No. 5,170,833 issued Dec. 15, 1992 to M & I Door Systems Limited describes a relatively high speed roll-up door wherein the curtain is made from a relatively thin plastic or fabric sheet. The top end of the thin curtain is mounted to a rotatable curtain roll which is operatively connected to an electric door operator. Two vertical guide channels are arranged on opposite sides of the door opening and act to guide the flexible curtain along the correct path. Each guide channel is constructed of two guide plates which can be made of steel or aluminum. The door itself is provided with a rigid bottom bar which extends the width of the door opening and into the guide channels. A safety edge device of known construction is provided along a bottom of the bottom bar. Each end of the bottom bar can be provided with a strip of friction reducing material made of the aforementioned ultra-high molecular weight plastic. These plastic strips help to reduce friction between an end plate of the bottom bar and a flange of a front guide plate of each guide channel.
The roll-up door of the present invention is provided with relatively inexpensive, wear resistant fabric strips that are attached to the side edge sections of the flexible sheet forming the door. These strips which extend in a direction parallel to the side edges of the door curtain cover the sloping shoulders formed between the thicker side edge sections of the curtain and the relatively thin main area of the curtain. These fabric strips reduce the amount of friction between the side edge sections of the curtain and their respective guide channels.
It is an object of the present invention to provide a roll-up door that can be manufactured more easily and at less cost than the previously known flexible rubber roll-up doors described above. In a preferred embodiment of the present roll-up door, the thicker side edges sections of the curtain can generally be pulled under an impact force from the guide channels, often without significant damage to the curtain, and the friction reducing fabric strips assist in the release of the side edge sections from their respective channels.